diff --git a/trio/_tests/test_exports.py b/trio/_tests/test_exports.py
index 4a35a95528..6710a115e1 100644
--- a/trio/_tests/test_exports.py
+++ b/trio/_tests/test_exports.py
@@ -118,7 +118,16 @@ def no_underscores(symbols):
         )
         from mypy.api import run
 
-        res = run(["--config-file=", "--follow-imports=silent", str(tmpfile)])
+        res = run(
+            [
+                "--config-file=",
+                "--follow-imports=silent",
+                "--no-site-packages",
+                "--soft-error-limit=-1",
+                "--no-error-summary",
+                str(tmpfile),
+            ]
+        )
 
         # clean up created py.typed file
         if not py_typed_exists:  # pragma: no cover
@@ -294,11 +303,14 @@ def no_hidden(symbols):
                     "--config-file=",
                     "--follow-imports=silent",
                     "--disable-error-code=operator",
+                    "--no-site-packages",
                     "--soft-error-limit=-1",
                     "--no-error-summary",
                     str(tmpfile),
                 ]
             )
+            assert res[2] != 2, f"internal error in mypy {res}"
+
             # no errors
             if res[2] == 0:
                 continue